An analytical model of the evolution of a Stokes wave and its two Benjamin–Feir sidebands on nonuniform unidirectional current
Summary: An analytical weakly nonlinear model of Benjamin–Feir instability of a Stokes wave on nonuniform unidirectional current is presented. In contrast to the models based on versions of the cubic Schrodinger equation the current variations could be strong, which allows us to examine the blockage of waves. Waves may overpass the blocking barrier produced by strong adverse current. We find reasonable correspondence between the results of model simulations and available experimental results.
Nonlin. Processes Geophys., 22, 313-324, doi:10.5194/npg-22-313-2015, 2015
Two-dimensional numerical simulations of shoaling internal solitary waves at the ASIAEX site in the South China Sea
Summary: Two-dimensional numerical simulations of the shoaling of an internal solitary wave (ISW) in the South China Sea have been undertaken. Peak amplitudes are attained at depths of 250 and 600m. Horizontal resolutions of 50m are required to simulate the formation of a pedestal in shallow water behind the shoaling wave. At a depth of 200m, waves can exceed maximum ISW amplitudes by 50%. Sensitivity to the bathymetry and stratification and the effects of rotation are considered.
Nonlin. Processes Geophys., 22, 289-312, doi:10.5194/npg-22-289-2015, 2015
Oscillations in a simple climate–vegetation model
Summary: Our conceptual model describes global temperature and vegetation extent. We use elements from Daisyworld and classical energy balance models and add an ocean with sea ice. The model exhibits oscillatory behavior within a plausible range of parameter values. Its periodic solutions have sawtooth behavior that is characteristic of relaxation oscillations, as well as suggestive of Quaternary glaciation cycles. The model is one of the simplest of its kind to produce such oscillatory behavior.
Nonlin. Processes Geophys., 22, 275-288, doi:10.5194/npg-22-275-2015, 2015
Incidence and reflection of internal waves and wave-induced currents at a jump in buoyancy frequency
Nonlin. Processes Geophys., 22, 259-274, doi:10.5194/npg-22-259-2015, 2015
A novel method for analyzing the process of abrupt climate change
Summary: A novel method is created to detect the process of the abrupt change, which has not been mentioned yet in traditional research. By building an ideal time series with a transition process, the results show that the process could be detected clearly. When applied to a climate index, this method detects five processes, and all of them have reappeared via the “start-end states” phase diagram. Additionally, it is detectable that the persist time of the process is related to global warming.
Nonlin. Processes Geophys., 22, 249-258, doi:10.5194/npg-22-249-2015, 2015
Data assimilation experiments using diffusive back-and-forth nudging for the NEMO ocean model
Nonlin. Processes Geophys., 22, 233-248, doi:10.5194/npg-22-233-2015, 2015
Estimation of the total magnetization direction of approximately spherical bodies
Summary: We have developed a fast total-field anomaly inversion to estimate the magnetization direction of multiple sources with approximately spherical shapes and known centres. It requires neither the prior computation of any transformation-like reduction to the pole nor the use of regularly spaced data on a horizontal grid. The method contains flexibility to be implemented as a linear or non-linear inverse problem. Applications to synthetic and field data show the good performance of our method.
Nonlin. Processes Geophys., 22, 215-232, doi:10.5194/npg-22-215-2015, 2015
Improved variational methods in statistical data assimilation
Summary: We propose an improved method of data assimilation, in which measured data are incorporated into a physically based model. In data assimilation, one typically seeks to minimize some cost function; here, we discuss a variational approximation in which model and measurement errors are Gaussian, combined with an annealing method, to consistently identify a global minimum of this cost function. We illustrate this procedure with archetypal chaotic systems, and discuss higher-order corrections.
Nonlin. Processes Geophys., 22, 205-213, doi:10.5194/npg-22-205-2015, 2015
Analysis of stochastic model for nonlinear volcanic dynamics
Summary: We consider a dynamic model of the magma-plug system previously derived by Iverson R. M. et al. (2006, Nature, 444) under the influence of stochastic forcing. The effects of noise-induced shifts, pressure stabilization and localization of random trajectories have been revealed by increasing the noise intensity. It is demonstrated that the repetitive stick-slip motions of the magma-plug system in the case of stochastic forcing can be connected with drumbeat earthquakes.
Nonlin. Processes Geophys., 22, 197-204, doi:10.5194/npg-22-197-2015, 2015
Statistical optimization for passive scalar transport: maximum entropy production versus maximum Kolmogorov–Sinai entropy
Nonlin. Processes Geophys., 22, 187-196, doi:10.5194/npg-22-187-2015, 2015
Equilibrium temperature distribution and Hadley circulation in an axisymmetric model
Summary: At the Equator, where the heating is larger than that at other latitudes, air rises and diverges poleward in the upper troposphere, descending more or less at 30° latitude; this circulation is the Hadley cell. We studied the impact of different meridional and vertical temperature distributions on a few features of the Hadley cell. Some parameters show a regular dependence on these distributions; others remain rather stable with distributions, but when they change, they do it in an abrupt way.
Nonlin. Processes Geophys., 22, 173-185, doi:10.5194/npg-22-173-2015, 2015
Brief Communication: The double layer in the separatrix region during magnetic reconnection
Summary: The key finding is that an electron beam can be generated in the separatrix region as magnetic reconnection proceeds. This electron beam could trigger the ion-acoustic instability, and a double layer accompanied with electron holes can be found during the nonlinear evolution stage of this instability.
Nonlin. Processes Geophys., 22, 167-171, doi:10.5194/npg-22-167-2015, 2015
Evaluation of empirical mode decomposition for quantifying multi-decadal variations and acceleration in sea level records
Summary: The ability of empirical mode decomposition (EMD) to extract multi-decadal variability from sea level records is tested using three simulations, based on sinusoidal oscillations and climate indices. In all cases, the longest-period modes are significantly distorted, with incorrect amplitudes and phases. This affects the estimated acceleration computed from the longest periodic IMF. Additionally, in all cases, extra low-frequency modes uncorrelated with the prescribed variability are found.
Nonlin. Processes Geophys., 22, 157-166, doi:10.5194/npg-22-157-2015, 2015
Geometric and topological approaches to significance testing in wavelet analysis
Nonlin. Processes Geophys., 22, 139-156, doi:10.5194/npg-22-139-2015, 2015
Time-dependent Long's equation
Summary: Long's equation models the steady state of two-dimensional stratified flow over terrain. It has been used extensively to investigate the generation and properties of gravity waves and their impact on the structure constants of the atmosphere. In this paper we derive a time-dependent version of this equation which might be useful in the analysis of experimental data about gravity waves.
Nonlin. Processes Geophys., 22, 133-138, doi:10.5194/npg-22-133-2015, 2015
Propagation regimes of interfacial solitary waves in a three-layer fluid
Summary: We have derived exact analytical expressions for the coefficients of evolution equations of long wave motion in the three-layer fluid with arbitrary parameters of the layers and established interrelations of these equations for different interfaces. To our understanding, the core advancement is the clarification and mapping of the regimes of soliton appearance and propagation in this environment that is much more realistic for the description of ocean internal waves.
Nonlin. Processes Geophys., 22, 117-132, doi:10.5194/npg-22-117-2015, 2015
Estimation of flow velocity for a debris flow via the two-phase fluid model
Nonlin. Processes Geophys., 22, 109-116, doi:10.5194/npg-22-109-2015, 2015
Non-Gaussian interaction information: estimation, optimization and diagnostic application of triadic wave resonance
Summary: Non-Gaussian joint PDFs and Shannon negentropies allow for nonlinear correlations and synergetic interaction information among random variables. Third-order cross-cumulants (triadic correlations -- TCs) under pair-wise (total or partial) independence are maximized on projections and orthogonal rotations of the full PDF. Fourier analysis allows decomposing TCs as wave resonant triads working as non-Gaussian sources of dynamical predictability. An illustration is given in a minimal fluid model.
Nonlin. Processes Geophys., 22, 87-108, doi:10.5194/npg-22-87-2015, 2015
Fluctuations in a quasi-stationary shallow cumulus cloud ensemble
Nonlin. Processes Geophys., 22, 65-85, doi:10.5194/npg-22-65-2015, 2015
Site effect classification based on microtremor data analysis using a concentration–area fractal model
Nonlin. Processes Geophys., 22, 53-63, doi:10.5194/npg-22-53-2015, 2015